1. Field of the Invention
This invention relates to the preparation of alkali metal carboxyalkoxy succinates and in particular to the preparation of said succinates in hydrated form.
2. Description of the Prior Art
It is known that alkali metal carboxyalkoxy succinates are useful detergent components, particularly as builders in detergent formulations.
Generally, the salts useful as builders are alkali metal salts of acids which have the formula: ##STR1## wherein R is a carboxyalkoxy radical (--OR'COOH) having from two to about seven carbon atoms total, R' being a "divalent alkyl" structure(--(CH.sub.2).sub.n --) where n is 1-6. Examples of such acids are .alpha.-carboxymethoxy succinic acid where R' is methyl and n is 1, .alpha.-(1-carboxybutoxy) succinic acid where R' is butyl and n is 4, .alpha.-(2-methyl-3-carboxybutoxy) succinic acid, .alpha.-(1-carboxyhexoxy) succinic acid. .alpha.-carboxyisobutoxy succinic acid, and the like. A preferred acid has been found to be the above mentioned .alpha.-carboxymethoxy succinic acid.
The water soluble salts of a .alpha.-carboxyalkoxy succinic acid are very useful detergent builders. The preferred salts are the mono-, di- and trialkali metal salts of such acids due to their relative inexpensiveness and stability. Examples of such salts are .alpha.-carboxymethoxy succinic acid, monosodium salt; .alpha.-carboxymethoxy succinic acid; trisodium salt; .alpha.-(1-carboxyethoxy) succinic acid; tripotassium salt; .alpha.-carboxyisobutoxy succinic acid, dilithium salt; .alpha.-carboxymethoxy succinic acid, monocesium salt; .alpha.-(1-carboxypropoxy) succinic acid, dirubidium salt; .alpha.-carboxymethoxy succinic acid, tripotassium salt and the like. Normally, the sodium or potassium salts will be found most useful. However, other non-alkali metal salts may be found suitable such as the ammonium salts, alkylammonium salts, or the like.
The builders of this invention can be advantageously used with a wide variety of detergent actives or surfactants, including those known in the art as anionic, cationic, nonionic, ampholytic, and zwitterionic detergents as well as any suitable mixture of such detergents. When the resultant washing compositions are used in aqueous washing systems, the cleaning power of the formulation is enhanced in much the same way as when the commonly used polyphosphate builders are employed. Yet the present builder systems do not contribute to the eutrophication problems characteristic or phosphorus-containing builders.
It has been known that the carboxyalkoxy succinates are produced by reacting zinc or alkaline earth metal salts of maleic acid and an appropriate hydroxy organic acid. For example, salts of glycolic acid and maleic acid may be reacted in an aqueous medium, usually with enough zinc or alkaline earth metal hydroxide such as calcium hydroxide to produce a pH of at least about 8 and preferably higher than about 11 as measured initially at 25.degree. C. to produce .alpha.-carboxymethoxy succinic acid, calcium salt. When such a typical mixture is heated to reflux temperature and maintained at that temperature for about 2 hours a carboxymethoxy succinate salt of zinc or alkaline earth metal is produced. In the past, a typical calcium system as obtained at this point has been reacted with sodium carbonate at a moderate temperature of about 60.degree. C. for example, then cooled to room temperature following which suspended calcium carbonate is filtered off and the filtrate is evaporated to recover a particulate alkali metal carboxymethoxy succinate. Unfortunately, the product recovered at this point has the undesired characteristics of being hygroscopic and of having a low purity.
Accordingly, it is an object of the present invention to provide a method of providing a pure alkali metal carboxymethoxy succinate of high purity and which is not hygroscopic.
Another object of the present invention is to provide a process for minimizing the content of contaminant salts of maleic acid, fumaric acid or hydroxy organic acid in alkali metal carboxyalkoxy succinate.